(1) Field of the Invention
The present invention relates to a system and method for controlling rotation of a drive wheel for a vehicle. The present invention relates particularly to the system and method for controlling rotation of a drive wheel for a vehicle in which a slippage (slip rate in percentage) is calculated between a drive wheel and road surface during a vehicle run and controlling rotation of the drive wheel so as to increase a frictional force on both drive wheel and road surface.
(2) Background of the Art
In general, various kinds of driving force controlling systems applicable to vehicles have been proposed in which during a vehicle acceleration an optimum driving force is applied to a drive wheel without occurrence of slip.
In such kinds of driving force controlling systems, a rotation speed of the drive wheel at the time of the vehicle acceleration is controlled so as to become slightly higher than a running speed of the vehicle so that a frictional force between the drive wheel and road surface becomes maximum. That is to say, in a case where a so-called slippage derived from a difference between the speed of the drive wheel and the speed of the vehicle body is approximately from 10% to 20%, the frictional force becomes maximum. A side force against a side skid of a vehicle body indicates an appropriate value so that a maximum acceleration characteristic and vehicle body stability can be achieved.
One of such kinds of driving force controlling systems is exemplified by a Japanese Patent Application First Publication (Tokkai) sho No. 61-60331 published on Mar. 28, 1986.
In the above-identified Japanese Patent Application Publication, the means for controlling the rotational speed of the drive wheel includes a first throttle valve whose opening angle is adjusted in accordance with an accelerator pedal depression, a second throttle valve located downstream or upstream of the first throttle valve, and means for adjusting an opening angle of the second throttle valve, so that the rotation of the drive wheel is controlled according to the opening angle of the first throttle valve.
However, since, in the previously proposed driving force controlling system, the opening angle of the second throttle valve is adjusted merely in accordance with a slip state of the vehicle, the vehicle only returns to an originally possible slip state which is before the avoidance of the slip. Therefore, the system is susceptible to the occurrence of a similar slip. In addition, during control of the slip prevention, a corresponding relationship between the operation of the accelerator pedal and driving force of the engine becomes lost so that an unmatched feeling for the operation of the accelerator pedal with respect to the driving force is given to the vehicle driver.